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| Sexual Dimorphism Signatures In The Brains Of Humans And Other Primates |
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| SciMed - Biology | |||||||||||
| TS-Si News Service | |||||||||||
| Friday, 20 June 2008 17:00 | |||||||||||
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Uppsala, Sweden. New research identifies hundreds of biological differences between the sexes when it comes to gene expression in the cerebral cortex of humans and other primates. New findings show that some of these differences arose a very long time ago and have been preserved throughout primate evolution.
There are fundamental questions for neuroscience regarding the relative contribution of genetics versus environment to behavioral differences between the sexes. Examples of the physical, and more obvious, gender [N1] differences include average body size and weight, and genitalia design. A team of researchers from Sweden and the United States. Uppsala Universitet, Karolinska Institutet, and The University of Chicago conducted a high precision inventory of the differences in gene expression between the sexes [N2].
Humans and chimpanzees do not look much alike on the outside. However their genome differs only by an estimated 1.3 percent. Geneticists have known for quite a while that this is not definitive.
The crucial differences between the species lie in the translation of the genetic make-up in protein building.
The Primate order includes over 375 species. The family Hominidae includes the great apes, of which humans are a representative. There are others: two species of chimpanzees (Pan troglodytes and P. paniscus), two of gorillas (Gorilla gorilla and G. beringei) and the two species of orangutans (Pongo pygmaeus and P. abelii).
Researchers at the Max Planck Institute for Evolutionary Anthropology examined the activity of around 21,000 genes in the heart, liver, kidneys, testicles and brain of both species.
With regard to genetic structure and activity, the brain shows the smallest differences between humans and chimpanzees. This is true even though we differ predominantly from chimpanzees through brain functions such as speech and memory.
Because chimpanzees are our closest living relatives, the chimp genome is the most useful key to understanding human biology and evolution, next to the human genome itself.
Lead author Björn Reinius notes that the study does not determine whether these differences in gene expression are in any way functionally significant. Their particular study focuses on gene expression within the cerebral cortex — that area of the brain that is involved in such complex functions in humans and other primates as memory, attentiveness, thought processes, and language.
The team hypothesized that some of the conserved differences between the sexes might be partially explained by sexually dependent gene expression differences in the brain. They also speculated that if differences in gene expression between males and females are functionally important, they may be conserved in the evolution of primates. To measure the activity of specific genes, the products of genes (RNA) obtained from the brain of each animal were hybridized to microarrays containing thousands of DNA clones coding for thousands of genes. The authors also investigated DNA sequence differences among primates for genes showing different levels of expression between the sexes. Their overall results point to:
In this context, such evolutionary constraints are present to conserve certain traits in a species. Examples include sexual dimorphism, homology (similarity due to shared ancestry), and body plans. The investigators explicitly state that for this study they "… do not know what regulatory mechanisms are controling the sexually dimorphic expression of the genes that were identified …" They speculate that expression of some of these genes could be under the regulation of sex hormones. The team took some initial steps to identify the potential conservation of sex hormonal regulation by investigating the presence of estrogen alpha- and androgen response elements. They measured the conserved regions in human and macaque in the genes identified in the study but relegate their results as exploratory, pending further studies in these issues. The researchers conclude from their observations that some sexual differences in the occipital cortex at the gene expression level may be conserved during the evolution of primates. They cite multiple lines of research that have observed sex differences in behavioral and cognitive abilities in humans and other primates. However, they are cautious and avoid claiming that these differences are caused by biological changes present in the brain — labeling them as "not yet known". Since further study could yield prevalence data, the study of sex dimorphic genes may in the future shed light on the basis of various birth conditions, including neurological disorders and psychiatric diseases, with differing prevalence between the sexes. Such advances would be a natural consequence of identifying the precise role of sexually distinct expression profiles and their possible involvement in physiology, behavior and cognition. Research UpdateThis report has been extended with new findings from a later research study. For more information, see the TS-Si.org article, Sex-based Differences Found In Prenatal Brain.
FundingThis work was supported by grants from the Börströms Foundation to Jennifer A. Leonard and Elena Jazin, the Swedish Science Foundation to Elena Jazin, and the National Institutes of Health (NIH) to Yoav Gilad.
CitationAn Evolutionarily Conserved Sexual Signature in the Primate Brain. Björn Reinius, Peter Saetre, Jennifer A. Leonard, Ran Blekhman, Roxana Merino-Martinez, Yoav Gilad, Elena Jazin. (2008). PLoS Genetics 4(6): e1000100. doi: 10.1371 / journal.pgen.1000100
Download PDF Abstract The question of a potential biological sexual signature in the human brain is a heavily disputed subject. In order to provide further insight into this issue, we used an evolutionary approach to identify genes with sex differences in brain expression level among primates. We reasoned that expression patterns important to uphold key male and female characteristics may be conserved during evolution. We selected cortex for our studies because this specific brain region is responsible for many higher behavioral functions. We compared gene expression profiles in the occipital cortex of male and female humans (Homo sapiens, a great ape) and cynomolgus macaques (Macaca fascicularis, an old world monkey), two catarrhine species that show abundant morphological sexual dimorphism, as well as in common marmosets (Callithrix Jacchus, a new world monkey) which are relatively sexually monomorphic. We identified hundreds of genes with sex-biased expression patterns in humans and macaques, while fewer than ten were differentially expressed between the sexes in marmosets. In primates, a general rule is that many of the morphological and behavioral sexual dimorphisms seen in polygamous species, such as macaques, are typically less pronounced in monogamous species such as the marmosets. Our observations suggest that this correlation may also be reflected in the extent of sex-biased gene expression in the brain. We identified 85 genes with common sex-biased expression, in both human and macaque and 2 genes, X inactivation-specific transcript (XIST) and Heat shock factor binding protein 1 (HSBP1), that were consistently sex-biased in the female direction in human, macaque, and marmoset. These observations imply a conserved signature of sexual gene expression dimorphism in cortex of primates. Further, we found that the coding region of female-biased genes is more evolutionarily constrained compared to the coding region of both male-biased and non sex-biased brain expressed genes. We found genes with conserved sexual gene expression dimorphism in the occipital cortex of humans, cynomolgus macaques, and common marmosets. Genes within sexual expression profiles may underlie important functional differences between the sexes, with possible importance during primate evolution.
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Sexual Dimorphism Signatures In The Brains Of Humans And Other Primates Friday, 20 June 2008
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| Last Updated on Saturday, 24 October 2009 21:08 |
But could the differences between sexes constitute a signature of sex differences in the 
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